Phosphor and light source comprising such a phosphor

ABSTRACT

A phosphor with a garnet structure is distinguished by the addition of Si. It is suitable in particular for photon excitation by light sources with an emission between 250 and 550 nm.

TECHNICAL FIELD

The invention is based on a phosphor and light source having such aphosphor. It relates in particular to a garnet-based phosphor which issuitable for use in light sources such as LEDs and lamps.

PRIOR ART

DE-U 201 08 013 has already disclosed a phosphor and light sourcecomprising such a phosphor, in which a phosphor is a garnet of definedrare earths. The use of various rare earths provides the option ofsetting the color locus of the phosphor within certain limits. However,phosphors of this type, if Y is not the main component of the latticesite occupied by rare earths, are relatively unstable or ratherinefficient or have only a low absorption capacity. Although Al may bepartially replaced by Ga in the garnet, in particular with these knownphosphors with a color locus in the green spectral region, theexcitability and consequently also the efficiency of the conversion arenot satisfactory. A further restriction on the desired color locus of aknown garnet phosphor aimed at realizing a white LED is that arelatively high cerium concentration tends to be required for thispurpose, but this can only be realized with very considerable difficultyin terms of manufacturing technology.

Hitherto, a combination of a plurality of phosphors has had to be usedto realize defined color loci corresponding, for example, to a neutralwhite or warm white luminous color. This two-component system inprinciple has a number of drawbacks: the longer-wave phosphor generallyabsorbs the emission of the shorter-wave phosphor. Furthermore, theparticle sizes of the phosphors have to be matched to one another sothat no agglomeration or sedimentation occurs. An additional factor isthat the phosphors have to be very homogeneously mixed in an exactmixing ratio in order to avoid color locus fluctuations. Finally, theknown phosphors generally have different temperature dependencies, whichcan result in a color locus drift in the event of the LED being dimmedor at different ambient temperatures.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a phosphor which isdistinguished by being robust and highly sensitive in terms of theselection of color locus within a wide range of the chromaticitydiagram.

A further object is to produce a highly efficient, stable green phosphorwith a garnet structure for use in LEDs with full-color capability basedon a primary LED which emits at a short wavelength, for example in theblue, with a long service life.

A further object is to produce a highly efficient garnet phosphor withan accurately matched color locus for photon excitation, in particularby white LEDs, and also to provide a light source, in particular a whiteLED with a neutral to warm white luminous color and with just onephosphor as converter. If a single phosphor is used, it is possible torestrict fluctuations in color locus and to simplify production, sincethere are no mixing and sedimentation problems. Of course, the phosphorcan also be used together with other phosphors to provide a lightsource.

This object is achieved by a phosphor with a garnet structure of typeA₃B₅O₁₂:D, characterized in that part of component B is replaced by Siin a proportion x, it being possible for at least one further component(KA, KB, KC) to be incorporated for charge compensation where A=rareearth and B=Al, Ga alone or in combination, and D=rare earth. In oneembodiment x=0.1 to 0.5. The substitution of component B, in particularAl³⁺, by Si⁴⁺ in accordance with the invention leads to a pronouncedcolor locus shift in phosphor systems with a garnet structure, forexample Y(Al, Ga)G:Ce. In this context, a further component is normallyalways required for reasons of charge compensation, since Si is atetravalent ion, but component B, such as for example Al, is a trivalention. For this reason, hitherto only the obvious route of replacing Alwith other trivalent ions, such as Ga or In, which occupy the samelattice site, has ever been investigated.

There are a number of ways of realizing this. In a first embodiment, anion KB which occupies the same lattice site but has a valence of lessthan 3, i.e. a monovalent or divalent ion, such as for example Mg²⁺, isintroduced simultaneously with Si. Another possible option is Be²⁺, forexample. In these cases, the replacement ion KB is often introduced asan oxide, so that no further charge compensation is required on accountof the garnet structure.

In a second embodiment, a different route is taken, in that an ion KCwhich occupies a different lattice site of opposite charge polarity isintroduced simultaneously with Si. On account of the different chargepolarity, in this case, there is no restriction on the choice ofvalence. In this case, it is particularly preferable for oxygen (to beunderstood as meaning O²⁻) to be replaced by nitrogen (to be understoodas meaning N³⁻).

In a third embodiment, an ion KA which occupies a different latticesite, namely that of component A, is introduced simultaneously with Si.In this case, the charge polarity is once again the same as that of Si.Examples of suitable candidates include Na and Li.

In a fourth embodiment, no further ion is introduced with Si, but ratherthe charge compensation is effected by means of vacancies (designated inaccordance with Kröger-Vink as V_(A) or V_(B) or V_(C) if the vacancy isat the lattice site of A, B or O), which are considered to have theirown valence of zero.

In general terms, ions whose radius is as close as possible to theradius of the ion to be replaced are preferably suitable. In practice,it has been found that if the radius is larger the limit for this is30%, i.e. a radius which is 1.3 times greater. In the case of an ionwhose radius is smaller than that of the ion to be replaced, this limitis much less critical.

The substitution while maintaining the garnet structure has nothing todo with the new types of nitridosilicates, which, although they may becomposed of similar individual components, have a completely differentstoichiometry, lattice structure and emission performance; a typicallattice structure is α-sialon, cf. “On new rare-earth doped M—Si—Al—O—Nmaterials”, van Krevel, T U Eindhoven 2000, ISBN 90-386-2711-4, Chapter2.

In detail, in the case of simultaneous charge compensation by exchangingO²⁻ for N³⁻, a significantly shorter-wave emission is found than for acorresponding garnet with conventional partial replacement of the Alwith Ga, i.e. Y(Al, Ga)G:Ce, as has hitherto been known from theliterature. The high quantum efficiency of the pure YAG:Ce phosphor isin this case virtually retained. By way of example, it is possible tosynthesize phosphors containing 4 mol % of cerium as activator and witha dominant wavelength of between 559 nm and 573 nm with a quantumefficiency of approx. 85-90%. Without the use of silicon, the ceriumdoping would have to be very greatly reduced to achieve comparabledominant wavelengths. With a 4% cerium doping, in practice 563 nm wasthe shortest dominant wavelength achieved. The cerium doping is in therange from 0.1 to 10%.

Surprisingly, the substitution acts differently in pure Al—containinggarnet phosphors of the (Y, Tb, Gd)AG:Ce type. Slight substitution (<1mol %) of Al by Si in YAG:Ce makes it possible to shift the dominantwavelength a few nanometers toward longer wavelengths without theefficiency of the phosphor decreasing. As a result, it is possible to“optimally” set the white color locus of the standard white LED withouthaving to use a second, generally less efficient phosphor for colorlocus correction.

If the silicon content is increased to up to 20 mol %, in particular inthe range from 1-20 mol %, preferably up to 10 mol %, an ever moreclearly visible red cerium emission is obtained. As a result, thedominant wavelength is shifted to up to 584 nm. It is found that whenusing a phosphor of this type, by way of example, it is possible toproduce a warm white LED with a color temperature of approx. 3200 K andan Ra value around 75-80 with just one phosphor. The quantum efficiencyof the phosphor rises with a decreasing Si content. Therefore, thecorresponding LED efficiency rises with an increasing color temperature.It is possible to realize light sources which are in the range ofluminous colors from similar to daylight through neutral white to warmwhite, in particular in the color temperature range from 2600 to 6500 K.

In this context, of course, the term garnet structure is also intendedto encompass a structure which deviates slightly from an ideal garnetand is based on vacancies or lattice disturbances, provided that thiscrystal retains the typical garnet structure.

A typical phosphor according to the invention has the ideal garnetstructure A₃B₅O₁₂:D with the novel basic modification in which Si ispositioned only on the lattice site of component B, and chargeneutrality needs to be maintained, for example realized asA₃B_(5−x)Si_(x)(KA,KB,KC)_(y)O_(12−y):D, with

A=rare earth (RE) selected from the group consisting of Y, Gd, Tb, La,Lu, individually or in combination;

B=Al, Ga, individually or in combination;

D=activator which replaces RE, selected from the group consisting of Ce,Pr, Eu, individually or in combination;

(KA, KB, KC)=charge compensator, selected in particular from Mg²⁺, Be²⁺and N³⁻, which compensates for the charge mismatch of the Si.

In this context, in particular the following relationships apply: 0<x≦1and 0≦y≦2x.

The value of y depends on the specific details of the crystal structure,in particular if the charge compensator is N, y=x.

In general, it should specifically be taken into account that differentlattice sites may have different valencies, and consequently a formationof the modified garnet taking account of possible compensatingcomponents KA on lattice site A, compensating components KB on latticesite B and compensating components KC on the lattice site of the oxygenleads to the general formula[A_(3−a)KA_(a)]_(A)[B_(5−b−x)KB_(b)Si_(x)]_(B)[O_(12−s)KC_(s)]o:D inwhich the activator D is to be counted as part of component A. In otherwords, therefore, the formula can also be expressed as[A_(3−t−a#)KA_(a#)D_(t)]_(A)[B_(5−b−x)KB_(b)Si_(x)]_(B)[O_(12−s)KC_(s)]_(O).In this formula, a# is a different value than a, which results fromincorporating the doping D in a, in a manner which is known per se.

The main condition for the coefficients can in general be presented asfollows:a(m _(KA)−3)+b(m _(KB)−3)+x=s(−m _(KC)−2).

In the above, m is the respective valence of the incorporated ion ofcomponent KA, KB or KC, with any vacancies being assumed to have avalence m=0.

In this context, there are a plurality of possible embodiments:

Firstly, there is the type in which Si replaces part of element B, withSi being introduced by a ferry, namely an oxygen-replacing mechanism,for example by means of nitrogen, so that the following formula appliesfor stoichiometry: A₃B_(5−x)Si_(x)[O_(12−s)N_(s)]_(O):D, in which thesubscript index O makes a statement about the lattice site O. Here, N isan ion of type KC, with in particular s≦1.5 and x≦1.5, and preferablyx=s.

Secondly, there is the type in which Si partially replaces the elementB, Si being introduced by a mechanism which compensates for the chargeat lattice site B, so that the following formula applies forstoichiometry: A₃[B_(5−(x+b))Si_(x)KB_(b)]_(B)O₁₂:D, in which thesubscript index B makes a statement about the lattice site B. By way ofexample, Si is introduced together with Mg or Na, specifically both viaan oxygen compound as ferry, wherein in particular b≦1 and x≦1.

In the case of a different form of introduction of the co-doping chargecompensator, for example by means of nitrogen or another element whichreplaces oxygen, the resulting stoichiometry gives a mixed form of thefirst type, i.e. for exampleA₃[B_(5−x−b)Si_(x)KB_(b)]_(B)[O_(12−s)N_(s]) _(O):D. One example is x=1and b=0.5 with B as Mg²⁺ and s=0.5.

Thirdly, there is the type in which Si partially replaces the element B,with Si being introduced by an element as a ferry which partiallyreplaces the lattice site A, i.e. being introduced by a mechanism whichreplaces A, so that the following formula applies for stoichiometry:

[A_(3−a)KA_(a)]_(A)[B_(5−x)Si_(x)]_(B)O₁₂:D, in which the subscriptindex A, B makes a statement about the association with the latticesites of components A and B. Here, in particular x=a. This behavior maymanifest itself in particular in the case of divalent ions, such as inparticular Mg or Be. However, Na and Li are also suitable as KA and areincorporated in monovalent form, in which case in particular a≦2 andx≦2.

Fourthly, there is the type which compensates for the chargecompensation solely by the formation of vacancies. In this case, the Sican be associated with vacancies at all lattice sites. The stoichiometryis then: A_(3−x/3)B_(5−x)Si_(x)O₁₂:D, in which in particular x≦0.2. Byway of example, x=0.1.

Of course, mixed forms of all these basic types may also occur. Thedoping D is normally always to be considered a constituent of latticesite A.

If B=Al, the value x is preferably between 0.01≦x≦1, and in the case ofB=(Al, Ga) with a Ga content of at least 20 mol % of B, the value of xis preferably in the range of from 0.05≦x≦0.25. Depending on thesurrounding conditions, the addition of Si in the garnet structureeffects a red or blue shift compared to an Si-free garnet of the sametype. Even more surprising is the discovery that the magnitude of thecolor locus shift is not an unambiguous function of the addition of Si,but rather has more of a dependent relationship. Particularly greatshifts can be achieved with relatively low quantities of Si added(x=0.08 to 0.23). Moreover, however, the behavior in individual cases isalso dependent on the charge compensator K, in particular the questionof its associated lattice site.

The ion radius of the Si⁴⁺ is similar to that of the Al³⁺, andconsequently this component is relatively easy to incorporate instead ofAl³⁺. This is one of the main points justifying the surprisingly goodreplacement function. By contrast, the ion radius of Mg²⁺, which canserve as a charge compensator here, is significantly larger than that ofAl³⁺, and consequently it is less easy to incorporate instead of Al³⁺.Therefore, with the system Si⁴⁺−Mg²⁺, only a relatively small quantityof Si⁴⁺ can be added.

By contrast, the system Si⁴⁺ with N³⁻ as charge compensator is much lesscritical, since the nitrogen ion replaces an oxygen ion of approximatelythe same size. Therefore, with this system a relatively large quantityof Si⁴⁺ can be added.

It is advantageous that this mechanism can in part also perform the roleof the activator D with a view to a shift in the color locus, so thatrelatively small quantities of D are required compared to conventionalgarnets. This applies in particular if D=Ce.

Moreover, the excitability of the new types of phosphor extends over awide range from approximately 250 nm, preferably 300 nm, up toapproximately 550 nm, preferably 490 nm. There are maxima atapproximately 350 nm and approximately 460 nm. Therefore, this phosphoris suitable not only for excitation by UV or blue emitting primary lightsources, such as LEDs or conventional Hg-based discharge lamps, but alsofor light sources such as a discharge lamp based on an indiumlow-pressure discharge or also an indium high-pressure discharge, theresonance lines of which lie, for example, at 304, 325, 410 and 451 nm.

The emission behavior is dependent to a significant extent on the chargecompensator. By way of example, the use of nitrogen leads to anincreased covalent bond content; in the literature, a behavior of thistype is described as what is known as a nephelauxetic effect. Anincreased crystal field splitting may simultaneously be superimposed onthis effect, for example as a result of the higher charge of the N³⁻ ioncompared to the O²⁻ ion. The Si⁴⁺ ion, which is more highly charged thanAl³⁺, additionally influences these effects, in a direction which isdependent on the particular details.

The phosphor according to the invention is eminently suitable for use asa green phosphor.

One particular advantage of the phosphors according to the invention isthat they have a relatively low temperature quenching. It is surprisingthat a tetravalent ion such as Si can be incorporated at the latticesite of a trivalent ion without significant efficiency losses.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is to be explained in more detail below on the basis of aplurality of exemplary embodiments. In the drawings:

FIG. 1 shows a semiconductor component which serves as light source(LED) for white or green light;

FIG. 2 shows an illumination unit with phosphors in accordance with thepresent invention;

FIG. 3 shows the emission spectrum of a warm-white LED with Si garnet;

FIG. 4 shows the reflectance of an Si garnet;

FIG. 5 shows the emission properties of an Si garnet;

FIG. 6 shows the emission properties of a further Si garnet;

FIG. 7 shows the emission properties of a further Si garnet;

FIG. 8 shows the shift in the dominant wavelength of an Si garnet;

FIG. 9 shows a spectrum of an LED lamp

FIG. 10 shows a spectrum of an LED lamp

FIG. 11 shows a spectrum of an LED lamp

FIG. 12 shows the shift in the dominant wavelength of an Si garnet;

FIG. 13 shows the chromaticity diagram for a blue primary LED with Sigarnet system;

FIGS. 14-17 show an X-ray diffractogram for various Si garnets;

FIG. 18 shows an example of an OLED;

FIG. 19 shows a low-pressure lamp with indium fill using a garnet;

FIG. 20 shows the long-term stability of a warm-white LED.

PREFERRED EMBODIMENT OF THE INVENTION

For use in a warm-white LED together with a GaInN chip, by way ofexample a similar structure to that described in U.S. Pat. No. 5,998,925is used. The structure of a light source of this type for white light isspecifically shown in FIG. 1. The light source is a semiconductorcomponent (chip 1) of type InGaN with a peak emission wavelength of 460nm and a first and second electrical connection 2, 3 embedded in anopaque basic housing 8 in the region of a recess 9. One of theconnections 3 is connected to the chip 1 via a bonding wire 14. Therecess has a wall 17 which serves as reflector for the primary radiationof the chip 1. The recess 9 is filled with a potting compound 5, whichas its main constituents contains an epoxy casting resin (for example 80to 90% by weight) and phosphor pigments 6 (for example less than 15% byweight). Further small fractions are attributable, inter alia, toAerosil. The phosphor pigments consist of pigments of silicon-containinggarnet. These emit yellow light and are mixed with a remainder of theunconverted blue of the primary radiation to form white. The samestructure is also suitable for creating a green-emitting LED, in whichcase the blue primary radiation is completely converted.

FIG. 2 shows part of a surface-light fitting 20 as illumination unit. Itcomprises a common support 21, to which a cuboidal outer housing 22 isadhesively bonded. Its upper side is provided with a common cover 23.The cuboidal housing has cutouts in which individual semiconductorcomponents 24 are accommodated. They are UV-emitting light-emittingdiodes with a peak emission of typically 340 nm. The conversion intowhite light takes place by means of conversion layers which arepositioned directly in the casting resin of the individual LEDs, in asimilar manner to that described in FIG. 1, or layers 25 which arearranged on all surfaces which are accessible to the UV radiation. Theseinclude the inner surfaces of the side walls of the housing, of thecover and of the base part. The conversion layers 25 consist of threephosphors which emit in the red, green and blue spectral regions usingthe phosphors according to the invention.

First of all, Table 1 shows ion radii of a few important elements whichare incorporated in the garnet. The relative quantum efficiencies QE ofsome Si garnets of type Y(Al_(3−x)Si_(x)Ga₂)G:Ce (4%) are shown in Table2.

FIG. 3 shows the emission spectrum of a warm-white LED which uses asingle Si garnet as conversion agent. The primary radiation is 460 nm,resulting in a color temperature of 3250 K and a color rendering indexof 80.

FIG. 4 shows the reflectance of an Si garnet as a function of thewavelength. This garnet is Y₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1):Ce.

FIG. 5 shows the emission properties of an Si garnet (x=0.25), namelyY₃Al_(4.75)Si_(0.251)O_(11.75)N_(0.25):Ce, as a function of thewavelength (in nm) in direct comparison with the emission properties ofthe same garnet without the addition of Si (x=0), namely YAG:Ce. Theconsiderable shift in the peak wavelength is amazing. A typical valuefor the cerium doping is from 0.5 to 4% of A.

FIG. 6 shows the emission properties of the Si garnetTb₃(Al_(4.5)Si_(0.5))O_(11.5)N_(0.5):Ce as a function of the wavelength.FIG. 7 shows the emission properties of the Si garnet(Y_(0.55)Gd_(0.45))₃(Al_(4.5)Si_(0.5))O_(11.5)N_(0.5):Ce as a functionof the wavelength.

FIG. 8 shows the shift in the dominant wavelength (nm) as a function ofthe content x of Si at 460 nm for the phosphorY₃(Al_(5−x)Si_(x))(O_(12−x)N_(x)):Ce. Surprisingly, the maximum is atapproximately 0.25. Therefore, the function is not linear.

FIG. 9 shows the change in the efficiency and emission width of variousphosphors of type Y_(2.88)Ce_(0.12)Al₅O₁₂ (i.e. YAG:Ce) when AlO isexchanged for SiN.

FIG. 10 shows the change in efficiency and emission width for variousphosphors of type Y_(2.88)Ce_(0.12)Al₃Ga₂O₁₂ (i.e. Y(Al,Ga)G:Ce) when Siis added as SiN as a replacement for AlO. Surprisingly, the addition ofgallium makes the properties of this system completely different fromthose of pure YAG:Ce.

FIG. 11 shows the emission properties of an Si garnet (x=0.25) as afunction of the wavelength (in nm) as a direct comparison with theemission properties of the same garnet without the addition of Si (x=0).Not only the great shift in the peak wavelength but also the fact thatthis shift is in precisely the opposite direction to in FIG. 5, areamazing. The details of this unusual behavior are not yet fullyunderstood.

FIG. 12 shows the shift in the dominant wavelength (nm) as a function ofthe content x of Si at 460 nm excitation for the phosphorY₃(Al_(3−x)Ga₂Si_(x))O₁₂:Ce. Surprisingly, the maximum is atapproximately 0.25, and therefore the function is not linear.

FIG. 13 shows the chromaticity diagram (CIE) with the coordinates x, yfor a system composed of blue LED (peak emission at 450 to 470 nm) andSi garnets according to the invention. It can be seen that in the caseof conventional garnets, it is now possible for the first time torealize systems with a warm-white luminous color of typically 3200 or2850 K or below in a simple way by means of a single phosphor.Candidates for this phosphor are in particular Si garnets based on thegarnets (unshaded triangles) of the rare earths Y, Tb and Gd, which canbe shifted to the right toward longer wavelengths by means of theaddition of Si (solid triangles). Conversely, green LEDs can besuccessfully realized by adding Si to Ga-containing garnets (Al:Ga ratiois preferably between 0.5 and 2.5), starting from YAG:Ce, in which casethe peak wavelength migrates to the left toward shorter wavelengths.

Therefore, Si garnets are ideally suited to being specifically adaptedto customer's requirements.

FIG. 14 shows an X-ray diffractogram for YAG:Ce with an Si contentx=0.1, which illustrates the typical garnet structure, compared toconventional YAG:Ce, cf. lower bar. FIG. 15 shows the same for a Sicontent of x=0.25.

FIG. 17 shows an X-ray diffractogram for Y₃Al_(3−x)Ga₂Si_(x)O₁₂:Ce witha Si content x=0.25, which illustrates the typical garnet structure,compared to conventional YAG:Ce, cf. the lower bar, with an yttriumoxynitride being indicated as a second bar, but the structure of thismaterial is not suitable for the phosphor under investigation. FIG. 16shows the same for an Si content of x=0.5.

A typical production process is fundamentally based on the standardproduction of YAG:Ce, with the following example of a modification:

The batch is selected as follows in accordance with Table 3:

This batch is mixed for approx. 40 min in a mortar mill; it is thencalcined at 1460-1560° C. for several hours (typically 3 h). The precisetemperature depends on the composition and in particular on the additionof flux. Boric acid H₃BO₃ is typically added.

FIG. 18 shows a further application, as is already known in principlefrom U.S. Pat. No. 6,700,322. In this case, the phosphor according tothe invention is used in combination with an OLED. The light source isan organic light-emitting diode 31, comprising the actual organic sheet30 and a transparent substrate 32. The sheet 30 emits in particular blueprimary light, generated for example by means of PVK:PBD:Coumarin. Theemission is partially converted into yellow, secondary emitted light bya covering layer, formed from a layer 33 of the phosphor according tothe invention, so that overall a white emission is realized by colormixing of the primary and secondary emitted light. It is preferable forthe phosphor according to the invention to interact with a blue-greenprimary emission. This means that the primary emission is at 480 to 505nm peak wavelength. It may particularly preferably also be realized byan organic phosphor sheet which has two peaks, one in the blue at 430 to490 nm and another at 495 to 520 nm, so that overall the dominantwavelength is in the blue-green. This system achieves amazing colorrendering values (Ra better than 85) at a color temperature of from 4000K to 4600 K using just two phosphors (the sheet and the modified garnetphosphor). The OLED substantially comprises at least one layer of alight-emitting polymer or of what are known as small molecules betweentwo electrodes, which consist of materials that are known per se, suchas for example ITO as anode, and a highly reactive metal, such as forexample Ba or Ca, as cathode. A plurality of layers are often also usedbetween the electrodes, serving either as a hole transport layer (forexample Baytron-P, commercially available from HC Starck) or also serveas electron transport layers in the region of the small molecules.

The emitting polymers used are, for example, polyfluorenes or polyspiromaterials.

A further application for the phosphor according to the invention is influorescent lamps, where it is applied to the inner side of the bulb, asis known per se, if appropriate in combination with further phosphorswhich are known per se, such as for example halophosphates. In thiscase, the excitation is effected by means of the known Hg lines, inparticular at 254 nm.

One specific application is an indium lamp. FIG. 19 shows a low-pressuredischarge lamp 50 with a mercury-free gas fill 51 (in the form of adiagrammatic illustration) which contains an indium compound and abuffer gas similar to WO 02/10374, with a layer 52 of Si-containinggarnet having been applied to the lamp wall 53. The very particularadvantage of this arrangement is that this modified garnet is wellmatched to the indium radiation, since the latter has significantcomponents both in the UV and in the blue spectral region, both of whichare equally well absorbed by this garnet, which makes it superior to thepreviously known phosphors for this application. These known phosphorssignificantly absorb either only the UV radiation or the blue radiationof the indium, and consequently the indium lamp according to theinvention is significantly more efficient. This statement also appliesto an indium lamp based on high pressure, as is known per se from U.S.Pat. No. 4,810,938.

A further application is excitation in electroluminescent lamps by ablue or blue-green emitting electroluminescent phosphor with a peakemission between 440 and 520 nm.

FIG. 20 shows the good long-term stability of a warm-white LED using thephosphor discussed in FIG. 3. Both the light flux (FIG. 20 a) and thecolor coordinates x and y (FIGS. 20 b, 20 c) remain virtually stableover 500 hours.

TABLE 1 ion radii (typical value) in nm CN4 CN6 tetrahedral octahedralMg²⁺ — 0.07 Al³⁺ 0.04 0.05 Ga³⁺ 0.05 0.06 Si⁴⁺ 0.04 0.05 O²⁻ 0.12 0.13N³⁻ 0.13 0.17

TABLE 2 relative quantum efficiency for Y(Al_(3-x)Si_(x)Ga₂)G:Ce at 460nm excitation X (Si) rel. QE in % Dominant wavelength (nm) 0 100 5660.25 101 559 0.50 103 560 0.75 100 561

TABLE 3 Component Purity Source of procurement Y₂O₃ 4N Rhodia CeO₂ 3N5Rhodia Al₂O₃ 4N Alfa A Ga₂O₃ 5N Alfa A SiO₂ Aerosil Ox 50 H₃BO₃ Merck

1. A phosphor with a garnet structure and having a compositionrepresented by a formula[A_(3−a)KA_(a)]_(A)[B_(5−b−x)KB_(b)Si_(x)]_(B)[O_(12−s)KC_(s)]_(O):Dwherein A is a rare earth, B is selected from Al, Ga or a combinationthereof, part of B is replaced by Si in a proportion x, D is a rareearth, and KA, KB, KC are charge-compensating components located atlattice sites A, B and O, respectively; and in which the followingrelationship applies: a(m_(KA)−3)+b(m_(KB)−3)+x=s(−m_(KC)−2), where m isthe valence of the incorporated ion of the charge-compensatingcomponents and s>0.
 2. The phosphor of claim 1 wherein KC is N.
 3. Thephosphor of claim 2 wherein s≦1.5 and x≦1.5.
 4. The phosphor of claim 2wherein x=s.
 5. The phosphor of claim 1 wherein s≦2x.
 6. The phosphor ofclaim 1 wherein A=Y, Tb, Gd, La, or Lu, alone or in combination.
 7. Thephosphor of claim 1 wherein D=Ce, Pr, or Eu, alone or in combination. 8.The phosphor of claim 7 wherein D=Ce, Pr, or Eu, alone or incombination.
 9. The phosphor of claim 1 wherein x≦1.
 10. The phosphor ofclaim 1 wherein one or more of the elements Mg, N, Be, Na or Li functionas one of the charge compensators KA, KB, or KC.
 11. A phosphor with agarnet structure and having a composition represented by a formulaA_(3−x/3)B_(5−x)Si_(x)O₁₂:D wherein A is a rare earth, B is selectedfrom Al, Ga or a combination thereof, part of B is replaced by Si in aproportion x, and D is a rare earth.
 12. The phosphor of claim 11wherein x≦0.2.
 13. The phosphor of claim 11 wherein A=Y, Tb, Gd, La, orLu, alone or in combination.
 14. The phosphor of claim 11 wherein D=Ce,Pr, or Eu, alone or in combination.
 15. The phosphor of claim 13 whereinD=Ce, Pr, or Eu, alone or in combination.
 16. A phosphor with a garnetstructure and having a composition represented by a formulaA₃B_(5−x)Si_(x)[O_(12−s)N_(s)]_(O):D wherein A is a rare earth, B isselected from Al, Ga or a combination thereof, part of B is replaced bySi in a proportion x, D is a rare earth and 0<s≦2x.
 17. The phosphor ofclaim 16 wherein s≦1.5 and x≦1.5.
 18. The phosphor of claim 16 whereinx=s.
 19. The phosphor of claim 16 wherein A=Y, Tb, Gd, La, or Lu, aloneor in combination.
 20. The phosphor of claim 16 wherein D=Ce, Pr, or Eu,alone or in combination.
 21. The phosphor of claim 19 wherein D=Ce, Pr,or Eu, alone or in combination.
 22. The phosphor of claim 1 whereinx=0.1 to 0.5.
 23. A light source comprising the phosphor as claimed inclaim 1, in which the primary emission of the light source serves toexcite the phosphor and a maximum of the primary emission is in therange from 250 to 550 nm, and in which the primary radiation is at leastpartially converted into secondary radiation, in particular in order togenerate white light.
 24. The light source as claimed in claim 23,characterized in that the light source is an LED or OLED or dischargelamp.